Effects of horizontal drains on slope stability under rainfall by three-dimensional finite element analysis

The effects of the horizontal drains on the ground water level during rainfall are predicted using a three-dimensional finite element analyses of transient water how through unsaturated-saturated soils. The slope stability is evaluated by the global safety factor, based on the three-dimensional elasto-plastic shear strength reduction finite element method. The following conclusions are obtained: (1) the horizontal drains can effectively lower the ground water level and increase the slope stability under rainfall, but the rate of the increase in the safety factor becomes smaller and smaller when the drains is extended beyond a critical length; (2) lengthening the horizontal drains is more effective than making the spacing smaller and increasing the number of the drains in a group in order to lower the ground water level and increase the slope stability; (3) the effects of the drains are mainly influenced by the ratio of the rainfall intensity to the saturated hydraulic conductivity. (C) 1999 Elsevier Science Ltd. All rights reserved.